Micro-electromechanical fluid ejection device having a chamber that is volumetrically altered for fluid ejection

ABSTRACT

An ink jet printhead chip includes a substrate. A plurality of nozzle arrangements is positioned on the substrate. Each nozzle arrangement includes a nozzle chamber and an ink ejection port in fluid communication with the nozzle chamber. An actuator is connected to the substrate and is displaceable with respect to the substrate. An ink ejection mechanism is connected to the actuator and is operatively arranged with respect to the nozzle chamber to eject ink from the ink ejection port on displacement of the actuator. The actuator has an actuating arm that has active beams that are configured to be displaced upon receipt of the control signal. The active beams are spaced from corresponding passive beams in a plane that spans the substrate. The spacing is greater than one percent of a length of the actuating arm and less than twenty percent of the length of the actuating arm.

[0001] Continuation application of U.S. Ser. No. 10/309,080 filed onDec. 4, 2002

FIELD OF THE INVENTION

[0002] The present invention relates to micro-electromechanical fluidejection devices.

BACKGROUND OF THE INVENTION

[0003] Many different types of printing have been invented, a largenumber of which are presently in use. The known forms of printers have avariety of methods for marking the print media with relevant markingmedia. Commonly used forms of printing include offset printing, laserprinting and copying devices, dot matrix type impact printers, thermalpaper printers, film recorders, thermal wax printers, dye sublimationprinters and ink jet printers both of the drop on demand and continuousflow type. Each type of printer has its own advantages and problems whenconsidering cost, speed, quality, reliability, simplicity ofconstruction and operation etc.

[0004] In recent years, the field of ink jet printing, wherein eachindividual pixel of ink is derived from one or more ink nozzles hasbecome increasingly popular primarily due to its inexpensive andversatile nature.

[0005] Many different techniques on ink jet printing have been invented.For a survey of the field, reference is made to an article by J Moore,“Non-Impact Printing: Introduction and Historical Perspective”, OutputHard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).

[0006] Ink Jet printers themselves come in many different types. Theutilisation of a continuous stream of ink in ink jet printing appears todate back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hanselldiscloses a simple form of continuous stream electro-static ink jetprinting.

[0007] U.S. Pat. No. 3,596,275 by Sweet also discloses a process ofcontinuous ink jet printing including the step wherein the ink jetstream is modulated by a high frequency electrostatic field so as tocause drop separation. This technique is still utilized by severalmanufacturers including Elmjet and Scitex (see also U.S. Pat. No.3,373,437 by Sweet et al)

[0008] Piezoelectric ink jet printers are also one form of commonlyutilized ink jet printing device. Piezoelectric systems are disclosed byKyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes adiaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970)which discloses a squeeze mode of operation of a piezoelectric crystal,by Stemme in U.S. Pat. No. 3,747,120 (1972) which discloses a bend modeof piezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 whichdiscloses a piezoelectric push mode actuation of the ink jet stream andby Fischbeck in U.S. Pat. No. 4,584,590 which discloses a shear modetype of piezoelectric transducer element.

[0009] Recently, thermal ink jet printing has become an extremelypopular form of ink jet printing. The ink jet printing techniquesinclude those disclosed by Endo et al in GB 2007162 (1979) and by Vaughtet al in U.S. Pat. No. 4,490,728. Both the aforementioned reference inkjet printing techniques rely upon the activation of an electrothermalactuator which results in the creation of a bubble in a constrictedspace, such as a nozzle, which thereby causes the ejection of ink froman aperture in communication with the confined space onto a relevantprint media. Manufacturers such as Canon and Hewlett Packard manufactureprinting devices utilizing the electrothermal actuator.

[0010] As can be seen from the foregoing, many different types ofprinting technologies are available. Ideally, a printing technologyshould have a number of desirable attributes. These include inexpensiveconstruction and operation, high-speed operation, safe and continuouslong-term operation etc. Each technology may have its own advantages anddisadvantages in the areas of cost, speed, quality, reliability, powerusage, simplicity of construction, operation, durability andconsumables.

[0011] In the construction of any inkjet printing system, there are aconsiderable number of important factors which must be traded offagainst one another especially as large scale printheads areconstructed, especially those of a pagewidth type. A number of thesefactors are outlined in the following paragraphs.

[0012] Firstly, inkjet printheads are normally constructed utilizingmicro-electromechanical systems (MEMS) techniques. As such, they tend torely upon the standard integrated circuit construction/fabricationtechniques of depositing planar layers on a silicon wafer and etchingcertain portions of the planar layers. Within silicon circuitfabrication technology, certain techniques are better known than others.For example, the techniques associated with the creation of CMOScircuits are likely to be more readily used than those associated withthe creation of exotic circuits including ferroelectrics, galliumarsenide etc. Hence, it is desirable, in any MEMS construction, toutilize well-proven semi-conductor fabrication techniques that do notrequire the utilization of any “exotic” processes or materials. Ofcourse, a certain degree of trade off will be undertaken in that if theuse of the exotic material far outweighs its disadvantages then it maybecome desirable to utilize the material anyway.

[0013] With a large array of ink ejection nozzles, it is desirable toprovide for a highly automated form of manufacturing which results in aninexpensive production of multiple printhead devices.

[0014] Preferably, the device constructed utilizes a low amount ofenergy in the ejection of ink. The utilization of a low amount of energyis particularly important when a large pagewidth full color printhead isconstructed having a large array of individual print ejection mechanismswith each ejection mechanism, in the worst case, being fired in a rapidsequence.

[0015] In the parent application, namely U.S. application Ser. No.09/113,122 there is disclosed a printhead chip having a plurality ofnozzle arrangements. These nozzle arrangements each include an actuator.The actuator has two pairs of actuating arms, each pair comprising anactive actuating arm and a passive actuating arm. The active actuatingarms are configured so that when heated upon receipt of an electricalsignal, they deform and drive an ink displacement mechanism so that inkcan be ejected from the respective nozzle chambers. The passiveactuating arms serve to provide resilient flexibility and stability tothe actuator.

[0016] The Applicant has found that it is desirable that the actuatorhas a certain configuration to avoid buckling of the actuator when theactive actuating arms are deformed to displace the actuator. Whileavoiding buckling, this configuration must also maintain efficiency ofthe actuator. This configuration is the subject of this invention.

SUMMARY OF THE INVENTION

[0017] According to a first aspect of the invention, there is provided amicro-electromechanical fluid ejection device that comprises

[0018] a substrate that defines a fluid inlet channel and incorporates awafer and CMOS layers positioned on the wafer;

[0019] a wall that extends from the substrate and bounds the fluid inletchannel;

[0020] an elongate actuator that is connected at one end to the CMOSlayers, an opposite end of the actuator being displaceable towards andaway from the substrate on receipt of an electrical signal from the CMOSlayers; and

[0021] a nozzle that is connected to said opposite end of the actuator,the nozzle having a crown portion and a skirt portion that depends fromthe crown portion, the crown portion defining a fluid ejection port andthe skirt portion being positioned so that the nozzle and the walldefine a chamber in fluid communication with the fluid inlet channel anda volume of the fluid chamber is reduced and subsequently enlarged asthe nozzle is driven towards and away from the nozzle chamber by theactuator to eject fluid from the fluid ejection port.

[0022] An edge of the skirt portion may be positioned adjacent an edgeof the wall such that, when the chamber is filled with liquid, ameniscus is pinned by the edges of the skirt portion and the wall todefine a fluidic seal that inhibits the egress of liquid from betweenthe wall and the skirt as liquid is ejected from the fluid ejectionport.

[0023] The crown portion may include a rim that defines the fluidejection port, the rim providing an anchor point for a meniscus that isformed in the fluid ejection port when the chamber is filled withliquid.

[0024] An arm interconnects said opposite end of the actuator and thenozzle.

[0025] The actuator may include a pair of active beams that are anchoredand electrically connected to the CMOS layers and a flexible passivestructure that is anchored to and electrically insulated from the CMOSlayers. Both the active beams and the passive structure may be connectedto the arm. The active beams may define a heating circuit and may be ofa thermally expandable material. The passive structure may be interposedbetween the active beams and the substrate such that, when the activebeams are heated by an electrical current, which is subsequently cutoff, the active beams expand and contract, causing said opposite end ofthe actuator and thus the arm and the nozzle to be driven towards andaway from the substrate.

[0026] The passive structure may be in the form of a pair of passivebeams of the same material as the active beams. The active beams may bespaced from the passive beams so that spacing between the active beamsand the passive beams is greater than one percent of a length of theactuator and less than twenty percent of the length of the actuator.

[0027] According to a second aspect of the invention, there is provideda micro-electromechanical fluid ejection device which comprises

[0028] a substrate that defines a plurality of fluid inlet channels andincorporates a wafer and CMOS layers positioned on the wafer;

[0029] walls that extend from the substrate to bound respective fluidinlet channels;

[0030] elongate actuators that are connected at one end to the CMOSlayers, an opposite end of each actuator being displaceable towards andaway from the substrate on receipt of an electrical signal from the CMOSlayers; and

[0031] nozzles that are connected to respective said opposite end of theactuators, each nozzle having a crown portion and a skirt portion thatdepends from the crown portion, the crown portion defining a fluidejection port and the skirt portion being positioned so that the nozzleand a respective wall define a chamber in fluid communication with thefluid inlet channel and a volume of the fluid chamber is reduced andsubsequently enlarged as the nozzle is driven towards and away from thenozzle chamber by the actuator to eject fluid from the fluid ejectionport.

[0032] In general, there is disclosed herein an ink jet nozzle assemblyincluding a nozzle chamber and a nozzle, the chamber including a movableportion and an actuating arm connected to or formed integrally with themovable portion and functioning in use to move said movable portionselectively to eject ink from the chamber via said nozzle, the actuatingarm having portions with equivalent thermal expansion characteristics soas to avoid differential thermal expansion in response to changes inambient temperature.

[0033] Preferably the actuating arm is formed of materials havingequivalent thermal expansion characteristics and a current is passedthrough only a portion of the actuating arm to effect said movement.

[0034] Preferably said nozzle chamber has an inlet in fluidcommunication with an ink reservoir. The nozzle chamber may include afixed portion configured with said movable portion such that relativemovement in an ejection phase reduces an effective volume of thechamber, and alternate relative movement in a refill phase enlarges theeffective volume of the chamber;

[0035] Portions of the actuating arms may be spaced apart and areadapted for selective differential thermal expansion upon heating so asto effect said relative movement.

[0036] The inlet may be positioned and dimensioned relative to thenozzle such that ink is ejected preferentially from the chamber throughsaid nozzle in droplet form in the ejection phase, and ink isalternately drawn preferentially into the chamber from the reservoirthrough the inlet in the refill phase.

[0037] Preferably, said movable portion includes the nozzle and thefixed portion is mounted on a substrate.

[0038] Preferably the actuating arm effectively extends between themovable portion and the substrate.

[0039] Preferably the fixed portion includes the nozzle mounted on asubstrate and the movable portion includes an ejection paddle.

[0040] Preferably the actuating arm is located substantially within thechamber.

[0041] Alternatively the actuating arm is located substantially outsidethe chamber.

[0042] Preferably the fixed portion includes a slotted sidewall in thechamber through which the actuating arm is connected to the movableportion.

[0043] Preferably the actuating arm has two portions that are ofsubstantially the same cross-sectional profile relative to one another.

[0044] Alternatively the portions of the actuating arm are of differentcross-sectional profiles relative to one another.

[0045] Preferably the portions are of substantially the same materialcomposition relative to one another.

[0046] Alternatively the portions are of different material compositionrelative to one another.

[0047] Preferably the portions are substantially parallel to oneanother.

[0048] Alternatively the portions are substantially non-parallel to oneanother.

[0049] Preferably one portion is adapted to be heated to a highertemperatures than the other portion in order to effect thermalactuation.

[0050] Preferably the respective portions are formed from multiplelayers of different material compositions disposed such that thermalexpansion or contraction in one portion due to the ambient temperaturefluctuations is balanced by a substantially corresponding thermalexpansion or contraction in the other portion.

[0051] Preferably the assembly is manufactured usingmicro-electro-mechanical-systems (MEMS) techniques.

[0052] Preferably an electric current is passed through one said portionarm and not the other said portion in use.

[0053] According to a first aspect of the invention, there is providedan ink jet printhead chip that comprises

[0054] a substrate;

[0055] a plurality of nozzle arrangements positioned on the substrate,each nozzle arrangement comprising

[0056] nozzle chamber walls that define a nozzle chamber and an inkejection port in fluid communication with the nozzle chamber;

[0057] an actuator that is connected to the substrate and isdisplaceable with respect to the substrate upon receipt of a controlsignal, the actuator being operatively arranged with respect to thenozzle chamber to eject ink from the ink ejection port on displacementof the actuator; wherein

[0058] the actuator includes an actuating arm that has at least oneactive portion that is configured to be displaced upon receipt of thecontrol signal and at least one corresponding passive portion, the, oreach, active portion being spaced from its corresponding passive portionin a plane that spans the substrate, so that spacing between the, oreach, active portion and its corresponding passive portion is greaterthan one percent of a length of the actuating arm and less than twentypercent of the length of the actuating arm.

[0059] The actuator may include at least two pairs of correspondingactive and passive portions.

[0060] Each active portion may be in the form of an elongate active beamand each passive portion may be in the form of an elongate passive beam.

[0061] The spacing between each active beam and its associated passivebeam may be greater than five percent of the length of the actuating armand less than ten percent of the length of the actuating arm.

[0062] The actuator may include an ink ejecting mechanism that isoperatively positioned with respect to the nozzle chamber. An end of theactuating arm may be anchored to the substrate and an opposed end of theactuating arm may be connected to the ink ejecting mechanism so thatdisplacement of the actuating arm results in the ink ejecting mechanismejecting ink from the ink ejection port.

[0063] The invention extends to an ink jet printhead, which comprises atleast one ink jet printhead chip as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Notwithstanding any other forms, which may fall within the scopeof the present invention, preferred forms of the invention will now bedescribed, by way of example only, with reference to the accompanyingdrawings in which:

[0065] FIGS. 1-3 illustrate the operational principles of the preferredembodiment;

[0066]FIG. 4 is a side perspective view of a single nozzle arrangementof the preferred embodiment;

[0067]FIG. 5 illustrates a sectional side view of a single nozzlearrangement;

[0068]FIGS. 6 and 7 illustrate operational principles of the preferredembodiment;

[0069] FIGS. 8-15 illustrate the manufacturing steps in the constructionof the preferred embodiment;

[0070]FIG. 16 illustrates a top plan view of a single nozzle;

[0071]FIG. 17 illustrates a portion of a single color printhead device;

[0072]FIG. 18 illustrates a portion of a three-color printhead device;

[0073]FIG. 19 provides a legend of the materials indicated in FIGS. 20to 29;

[0074]FIG. 20 to FIG. 29 illustrate sectional views of the manufacturingsteps in one form of construction of an ink jet printhead nozzle;

[0075]FIG. 30 shows a three dimensional, schematic view of a nozzleassembly for an ink jet printhead in accordance with another embodimentof the invention;

[0076] FIGS. 31 to 33 show a three dimensional, schematic illustrationof an operation of the nozzle assembly of FIG. 30;

[0077]FIG. 34 shows a three dimensional view of a nozzle arrayconstituting an ink jet printhead;

[0078]FIG. 35 shows, on an enlarged scale, part of the array of FIG. 34;

[0079]FIG. 36 shows a three dimensional view of an ink jet printheadincluding a nozzle guard;

[0080]FIGS. 37a to 37 r show three-dimensional views of steps in themanufacture of a nozzle assembly of an ink jet printhead;

[0081]FIGS. 38a to 38 r show sectional side views of the manufacturingsteps;

[0082]FIGS. 39a to 39 k show layouts of masks used in various steps inthe manufacturing process;

[0083]FIGS. 40a to 40 c show three dimensional views of an operation ofthe nozzle assembly manufactured according to the method of FIGS. 37 and38; and

[0084]FIGS. 41a to 41 c show sectional side views of an operation of thenozzle assembly manufactured according to the method of FIGS. 37 and 38.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

[0085] In the preferred embodiment, there is provided a nozzle chamberhaving ink within it and a thermal actuator device interconnected to anink ejecting mechanism in the form of a paddle, the thermal actuatordevice being actuated so as to eject ink from the nozzle chamber. Thepreferred embodiment includes a particular thermal actuator structurewhich includes an actuator arm in the form of a tapered heater structurearm for providing positional heating of a conductive heater layer row.The actuator arm is connected to the paddle through a slotted wall inthe nozzle chamber. The actuator arm has a mating shape so as to matesubstantially with the surfaces of the slot in the nozzle chamber wall.

[0086] Turning initially to FIGS. 1-3, there is provided schematicillustrations of the basic operation of the device. A nozzle chamber 1is provided filled with ink 2 by means of an ink inlet channel 3 whichcan be etched through a wafer substrate on which the nozzle chamber 1rests. The nozzle chamber 1 includes an ink ejection nozzle or aperture4 around which an ink meniscus forms.

[0087] Inside the nozzle chamber 1 is a paddle type device 7 which isconnected to an actuator arm 8 through a slot in the wall of the nozzlechamber 1. The actuator arm 8 includes a heater means 9 located adjacentto a post end portion 10 of the actuator arm. The post 10 is fixed to asubstrate.

[0088] When it is desired to eject a drop from the nozzle chamber, asillustrated in FIG. 2, the heater means 9 is heated so as to undergothermal expansion. Preferably, the heater means itself or the otherportions of the actuator arm 8 are built from materials having a highbend efficiency where the bend efficiency is defined as$\text{bend~~efficiency} = \frac{\text{Young's~~Modulus} \times \text{(Coefficient~~of~~thermal~~Expansion)}}{\text{Density} \times \text{Specific~~Heat~~Capacity}}$

[0089] A suitable material for the heater elements is a copper nickelalloy which can be formed so as to bend a glass material.

[0090] The heater means is ideally located adjacent the post end portion10 such that the effects of activation are magnified at the paddle end 7such that small thermal expansions near post 10 result in largemovements of the paddle end. The heating 9 causes a general increase inpressure around the ink meniscus 5 which expands, as illustrated in FIG.2, in a rapid manner. The heater current is pulsed and ink is ejectedout of the nozzle 4 in addition to flowing in from the ink channel 3.Subsequently, the paddle 7 is deactivated to again return to itsquiescent position. The deactivation causes a general reflux of the inkinto the nozzle chamber. The forward momentum of the ink outside thenozzle rim and the corresponding backflow results in a general neckingand breaking off of a drop 12 which proceeds to the print media. Thecollapsed meniscus 5 results in a general sucking of ink into the nozzlechamber 1 via the in flow channel 3. In time, the nozzle chamber isrefilled such that the position in FIG. 1 is again reached and thenozzle chamber is subsequently ready for the ejection of another drop ofink.

[0091] Turning now to FIG. 4, there is illustrated a single nozzlearrangement 20 of the preferred embodiment. The arrangement includes anactuator arm 21 which includes a bottom layer 22 which is constructedfrom a conductive material such as a copper nickel alloy (hereinaftercalled cupronickel) or titanium nitride (TiN). The layer 22, as willbecome more apparent hereinafter includes a tapered end portion near theend post 24. The tapering of the layer 22 near this end means that anyconductive resistive heating occurs near the post portion 24.

[0092] The layer 22 is connected to the lower CMOS layers 26 which areformed in the standard manner on a silicon substrate surface 27. Theactuator arm 21 is connected to an ejection paddle which is locatedwithin a nozzle chamber 28. The nozzle chamber 28 includes an inkejection nozzle 29 from which ink is ejected and includes a convolutedslot arrangement 30 which is constructed such that the actuator arm 21is able to move up and down while causing minimal pressure fluctuationsin the area of the nozzle chamber 28 around the slot 30.

[0093]FIG. 5 illustrates a sectional view through a single nozzle. FIG.5 illustrates more clearly the internal structure of the nozzle chamberwhich includes the paddle 32 attached to the actuator arm 21 having face33. Importantly, the actuator arm 21 includes, as noted previously, abottom conductive layer 22. Additionally, a top layer 25 is alsoprovided.

[0094] The utilization of a second layer 25 of the same material as thefirst layer 22 allows for more accurate control of the actuator positionas will be described with reference to FIGS. 6 and 7. In FIG. 6, thereis illustrated the example where a high Young's Modulus material 40 isdeposited utilizing standard semiconductor deposition techniques and ontop of which is further deposited a second layer 41 having a much lowerYoung's Modulus. Unfortunately, the deposition is likely to occur at ahigh temperature. Upon cooling, the two layers are likely to havedifferent coefficients of thermal expansion and different Young'sModuli. Hence, in ambient room temperature, the thermal stresses arelikely to cause bending of the two layers of material as shown at 42.

[0095] By utilizing a second deposition of the material having a highYoung's Modulus, the situation in FIG. 7 is likely to result wherein thematerial 41 is sandwiched between the two layers 40. Upon cooling, thetwo layers 40 are kept in tension with one another so as to result in amore planar structure 45 regardless of the operating temperature. Thisprinciple is utilized in the deposition of the two layers 22, 25 ofFIGS. 4-5.

[0096] Turning again to FIGS. 4 and 5, one important attribute of thepreferred embodiments includes the slotted arrangement 30. The slottedarrangement results in the actuator arm 21 moving up and down therebycausing the paddle 32 to also move up and down resulting in the ejectionof ink. The slotted arrangement 30 results in minimum ink outflowthrough the actuator arm connection and also results in minimal pressureincreases in this area. The face 33 of the actuator arm is extended outso as to form an extended interconnect with the paddle surface therebyproviding for better attachment. The face 33 is connected to a blockportion 36 which is provided to provide a high degree of rigidity. Theactuator arm 21 and the wall of the nozzle chamber 28 have a generallycorrugated nature so as to reduce any flow of ink through the slot 30.The exterior surface of the nozzle chamber adjacent the block portion 36has a rim eg. 38 so to minimize wicking of ink outside of the nozzlechamber. A pit 37 is also provided for this purpose. The pit 37 isformed in the lower CMOS layers 26. An ink supply channel 39 is providedby means of back etching through the wafer to the back surface of thenozzle.

[0097] Turning to FIGS. 8-15 there will now be described fabricationsteps utilized in the construction of a single nozzle in accordance withthe preferred embodiment.

[0098] The fabrication uses standard micro-electromechanical techniques.For a general introduction to a micro-electromechanical systems (MEMS)reference is made to standard proceedings in this field including theproceeding of the SPIE (International Society for Optical Engineering)including volumes 2642 and 2882 which contain the proceedings of recentadvances and conferences in this field.

[0099] 1. The preferred embodiment starts with a double sided polishedwafer complete with, say, a 0.2 μm 1 poly 2 metal CMOS process providingfor all the electrical interconnects necessary to drive the inkjetnozzle.

[0100] 2. As shown in FIG. 8, the CMOS wafer 26 is etched at 50 down tothe silicon layer 27. The etching includes etching down to an aluminumCMOS layer 51, 52.

[0101] 3. Next, as illustrated in FIG. 9, a 1 μm layer of sacrificialmaterial 55 is deposited. The sacrificial material can be aluminum orphotosensitive polyimide.

[0102] 4. The sacrificial material is etched in the case of aluminum orexposed and developed in the case of polyimide in the area of the nozzlerim 56 and including a dished paddle area 57.

[0103] 5. Next, a 1 μm layer of heater material 60 (cupronickel or TiN)is deposited.

[0104] 6. A 3.4 μm layer of PECVD glass 61 is then deposited.

[0105] 7. A second layer 62 equivalent to the first layer 60 is thendeposited.

[0106] 8. All three layers 60-62 are then etched utilizing the samemask. The utilization of a single mask substantially reduces thecomplexity in the processing steps involved in creation of the actuatorpaddle structure and the resulting structure is as illustrated in FIG.10. Importantly, a break 63 is provided so as to ensure electricalisolation of the heater portion from the paddle portion.

[0107] 9. Next, as illustrated in FIG. 11, a 10 μm layer of sacrificialmaterial 70 is deposited.

[0108] 10. The deposited layer is etched (or just developed ifpolyimide) utilizing a fourth mask which includes nozzle rim etchantholes 71, block portion holes 72 and post portion 73.

[0109] 11. Next a 10 μm layer of PECVD glass is deposited so as to formthe nozzle rim 71, arm portions 72 and post portions 73.

[0110] 12. The glass layer is then planarized utilizing chemicalmechanical planarization (CMP) with the resulting structure asillustrated in FIG. 11.

[0111] 13. Next, a 3 μm layer of PECVD glass is deposited.

[0112] 14. The deposited glass is then etched as shown in FIG. 12, to adepth of approximately 1 μm so as to form nozzle rim portion 81 andactuator interconnect portion 82.

[0113] 15. Next, as illustrated in FIG. 13, the glass layer is etchedutilizing a 6th mask so as to form final nozzle rim portion 81 andactuator guide portion 82.

[0114] 16. Next, as illustrated in FIG. 14, the ink supply channel isback etched 85 from the back of the wafer utilizing a 7th mask. The etchcan be performed utilizing a high precision deep silicon trench etchersuch as the STS Advanced Silicon Etcher (ASE). This step can also beutilized to nearly completely dice the wafer.

[0115] 17. Next, as illustrated in FIG. 15 the sacrificial material canbe stripped or dissolved to also complete dicing of the wafer inaccordance with requirements.

[0116] 18. Next, the printheads can be individually mounted on attachedmolded plastic ink channels to supply ink to the ink supply channels.

[0117] 19. The electrical control circuitry and power supply can then bebonded to an etch of the printhead with a TAB film.

[0118] 20. Generally, if necessary, the surface of the printhead is thenhydrophobized so as to ensure minimal wicking of the ink along externalsurfaces. Subsequent testing can determine operational characteristics.

[0119] Importantly, as shown in the plan view of FIG. 16, the heaterelement has a tapered portion adjacent the post 73 so as to ensuremaximum heating occurs near the post.

[0120] Of course, different forms of inkjet printhead structures can beformed. For example, there is illustrated in FIG. 17, a portion of asingle color printhead having two spaced apart rows 90, 91, with the tworows being interleaved so as to provide for a complete line of ink to beejected in two stages. Preferably, a guide rail 92 is provided forproper alignment of a TAB film with bond pads 93. A second protectivebarrier 94 can also preferably be provided. Preferably, as will becomemore apparent with reference to the description of FIG. 18 adjacentactuator arms are interleaved and reversed.

[0121] Turning now to FIG. 18, there is illustrated a full colorprinthead arrangement which includes three series of inkjet nozzles 95,96, 97 one each devoted to a separate color. Again, guide rails 98, 99are provided in addition to bond pads, eg. 100. In FIG. 18, there isillustrated a general plan of the layout of a portion of a full colorprinthead which clearly illustrates the interleaved nature of theactuator arms.

[0122] The presently disclosed ink jet printing technology ispotentially suited to a wide range of printing system including: colorand monochrome office printers, short run digital printers, high speeddigital printers, offset press supplemental printers, low cost scanningprinters high speed pagewidth printers, notebook computers with inbuiltpagewidth printers, portable color and monochrome printers, color andmonochrome copiers, color and monochrome facsimile machines, combinedprinter, facsimile and copying machines, label printers, large formatplotters, photograph copiers, printers for digital photographic“minilabs”, video printers, PHOTO CD (PHOTO CD is a registered trademarkof the Eastman Kodak Company) printers, portable printers for PDAs,wallpaper printers, indoor sign printers, billboard printers, fabricprinters, camera printers and fault tolerant commercial printer arrays.

[0123] One alternative form of detailed manufacturing process which canbe used to fabricate monolithic ink jet printheads operating inaccordance with the principles taught by the present embodiment canproceed utilizing the following steps:

[0124] 1. Using a double sided polished wafer 27, complete drivetransistors, data distribution, and timing circuits using a 0.5 micron,one poly, 2 metal CMOS process to form layer 26. Relevant features ofthe wafer at this step are shown in FIG. 20. For clarity, these diagramsmay not be to scale, and may not represent a cross section though anysingle plane of the nozzle. FIG. 19 is a key to representations ofvarious materials in these manufacturing diagrams, and those of othercross-referenced ink jet configurations.

[0125] 2. Etch oxide down to silicon or aluminum using Mask 1. This maskdefines the nozzle chamber, the surface anti-wicking notch 37, and theheater contacts 110. This step is shown in FIG. 21.

[0126] 3. Deposit 1 micron of sacrificial material 55 (e.g. aluminum orphotosensitive polyimide)

[0127] 4. Etch (if aluminum) or develop (if photosensitive polyimide)the sacrificial layer using Mask 2. This mask defines the nozzle chamberwalls 112 and the actuator anchor point. This step is shown in FIG. 22.

[0128] 5. Deposit 1 micron of heater material 60 (e.g. cupronickel orTiN). If cupronickel, then deposition can consist of three steps—a thinanti-corrosion layer of, for example, TiN, followed by a seed layer,followed by electroplating of the 1 micron of cupronickel.

[0129] 6. Deposit 3.4 microns of PECVD glass 61.

[0130] 7. Deposit a layer 62 identical to step 5.

[0131] 8. Etch both layers of heater material, and glass layer, usingMask 3. This mask defines the actuator, paddle, and nozzle chamberwalls. This step is shown in FIG. 23.

[0132] 9. Wafer probe. All electrical connections are complete at thispoint, bond pads are accessible, and the chips are not yet separated.

[0133] 10. Deposit 10 microns of sacrificial material 70.

[0134] 11. Etch or develop sacrificial material using Mask 4. This maskdefines the nozzle chamber wall 112. This step is shown in FIG. 24.

[0135] 12. Deposit 3 microns of PECVD glass 113.

[0136] 13. Etch to a depth of (approx.) 1 micron using Mask 5. This maskdefines the nozzle rim 81. This step is shown in FIG. 25.

[0137] 14. Etch down to the sacrificial layer using Mask 6. This maskdefines the roof 114 of the nozzle chamber, and the nozzle itself. Thisstep is shown in FIG. 26.

[0138] 15. Back-etch completely through the silicon wafer (with, forexample, an ASE Advanced Silicon Etcher from Surface Technology Systems)using Mask 7. This mask defines the ink inlets 30 which are etchedthrough the wafer. The wafer is also diced by this etch. This step isshown in FIG. 27.

[0139] 16. Etch the sacrificial material. The nozzle chambers arecleared, the actuators freed, and the chips are separated by this etch.This step is shown in FIG. 28.

[0140] 17. Mount the printheads in their packaging, which may be amolded plastic former incorporating ink channels which supply theappropriate color ink to the ink inlets at the back of the wafer.

[0141] 18. Connect the printheads to their interconnect systems. For alow profile connection with minimum disruption of airflow, TAB may beused. Wire bonding may also be used if the printer is to be operatedwith sufficient clearance to the paper.

[0142] 19. Hydrophobize the front surface of the printheads.

[0143] 20. Fill the completed printheads with ink 115 and test them. Afilled nozzle is shown in FIG. 29.

[0144] Referring now to FIG. 30 of the drawings, a nozzle assembly, inaccordance with a further embodiment of the invention is designatedgenerally by the reference numeral 110. An ink jet printhead has aplurality of nozzle assemblies 110 arranged in an array 114 (FIGS. 34and 35) on a silicon substrate 116. The array 114 will be described ingreater detail below.

[0145] The assembly 110 includes a silicon substrate or wafer 116 onwhich a dielectric layer 118 is deposited. A CMOS passivation layer 120is deposited on the dielectric layer 118.

[0146] Each nozzle assembly 110 includes a nozzle 122 defining a nozzleopening 124, a connecting member in the form of a lever arm 126 and anactuator 128. The lever arm 126 connects the actuator 128 to the nozzle122.

[0147] As shown in greater detail in FIGS. 31 to 33 of the drawings, thenozzle 122 comprises a crown portion 130 with a skirt portion 132depending from the crown portion 130. The skirt portion 132 forms partof a peripheral wall of a nozzle chamber 134 (FIGS. 31 to 33 of thedrawings). The nozzle opening 124 is in fluid communication with thenozzle chamber 134. It is to be noted that the nozzle opening 124 issurrounded by a raised rim 136 which “pins” a meniscus 138 (FIG. 31) ofa body of ink 140 in the nozzle chamber 134.

[0148] An ink inlet aperture 142 (shown most clearly in FIG. 35 of thedrawing) is defined in a floor 146 of the nozzle chamber 134. Theaperture 142 is in fluid communication with an ink inlet channel 148defined through the substrate 116.

[0149] A wall portion 150 bounds the aperture 142 and extends upwardlyfrom the floor portion 146. The skirt portion 132, as indicated above,of the nozzle 122 defines a first part of a peripheral wall of thenozzle chamber 134 and the wall portion 150 defines a second part of theperipheral wall of the nozzle chamber 134.

[0150] The wall 150 has an inwardly directed lip 152 at its free endwhich serves as a fluidic seal which inhibits the escape of ink when thenozzle 122 is displaced, as will be described in greater detail below.It will be appreciated that, due to the viscosity of the ink 140 and thesmall dimensions of the spacing between the lip 152 and the skirtportion 132, the inwardly directed lip 152 and surface tension functionas a seal for inhibiting the escape of ink from the nozzle chamber 134.

[0151] The actuator 128 is a thermal bend actuator and is connected toan anchor 154 extending upwardly from the substrate 116 or, moreparticularly, from the CMOS passivation layer 120. The anchor 154 ismounted on conductive pads 156 which form an electrical connection withthe actuator 128.

[0152] The actuator 128 comprises an actuator arm in the form of a pairof active beams 158 arranged above a pair of passive beams 160. In apreferred embodiment, both beams 158 and 160 are of, or include, aconductive ceramic material such as titanium nitride (TiN).

[0153] The beams 158 and 160 have their first ends anchored to theanchor 154 and their opposed ends connected to the arm 126. When acurrent is caused to flow through the active beams 158 thermal expansionof the beams 158 results. As the passive beams 160, through which thereis no current flow, do not expand at the same rate, a bending moment iscreated causing the arm 126 and, hence, the nozzle 122 to be displaceddownwardly towards the substrate 116 as shown in FIG. 32 of thedrawings. This causes an ejection of ink through the nozzle opening 124as shown at 162 in FIG. 32 of the drawings. Thus, the nozzle 122 and thearm 126 define an ink ejecting mechanism. When the source of heat isremoved from the active beams 158, i.e. by stopping current flow, thenozzle 122 returns to its quiescent position as shown in FIG. 33 of thedrawings. When the nozzle 122 returns to its quiescent position, an inkdroplet 164 is formed as a result of the breaking of an ink droplet neckas illustrated at 166 in FIG. 33 of the drawings. The ink droplet 164then travels on to the print media such as a sheet of paper. As a resultof the formation of the ink droplet 164, a “negative” meniscus is formedas shown at 168 in FIG. 33 of the drawings. This “negative” meniscus 168results in an inflow of ink 140 into the nozzle chamber 134 such that anew meniscus 138 (FIG. 31) is formed in readiness for the next ink dropejection from the nozzle assembly 110.

[0154] Each active beam 158 corresponds with one passive beam 160 toform two pairs of beams comprising an active beam 158 and acorresponding passive beam 160. Each active beam 158 is spaced from itscorresponding passive beam 160 in a plane that is substantially parallelto the substrate. The spacing between each active beam 158 and itsrespective passive beam 160 is suitably between 1 percent and 20 percentof the length of the beams. Preferably the spacing is between 5 percentand 10 percent of the length of the beams. The Applicant has found thatthis configuration provides the best protection against mutual bucklingwhile maintaining efficiency of operation. In particular, Applicant hasfound that if the spacing is less than 1 percent of the length of thebeams there is an unacceptable risk of mutual buckling and if thespacing is greater than 20 percent of the length of the beams theefficiency of the actuators 128 is compromised.

[0155] Referring now to FIGS. 34 and 35 of the drawings, the nozzlearray 114 is described in greater detail. The array 114 is for afour-color printhead. Accordingly, the array 114 includes four groups170 of nozzle assemblies, one for each color. Each group 170 has itsnozzle assemblies 110 arranged in two rows 172 and 174. One of thegroups 170 is shown in greater detail in FIG. 35 of the drawings.

[0156] To facilitate close packing of the nozzle assemblies 110 in therows 172 and 174, the nozzle assemblies 110 in the row 174 are offset orstaggered with respect to the nozzle assemblies 110 in the row 172.Also, the nozzle assemblies 110 in the row 172 are spaced apartsufficiently far from each other to enable the lever arms 126 of thenozzle assemblies 110 in the row 174 to pass between adjacent nozzles122 of the assemblies 110 in the row 172. It is to be noted that eachnozzle assembly 110 is substantially dumbbell shaped so that the nozzles122 in the row 172 nest between the nozzles 122 and the actuators 128 ofadjacent nozzle assemblies 110 in the row 174.

[0157] Further, to facilitate close packing of the nozzles 122 in therows 172 and 174, each nozzle 122 is substantially hexagonally shaped.

[0158] It will be appreciated by those skilled in the art that, when thenozzles 122 are displaced towards the substrate 116, in use, due to thenozzle opening 124 being at a slight angle with respect to the nozzlechamber 134 ink is ejected slightly off the perpendicular. It is anadvantage of the arrangement shown in FIGS. 34 and 35 of the drawingsthat the actuators 128 of the nozzle assemblies 110 in the rows 172 and174 extend in the same direction to one side of the rows 172 and 174.Hence, the ink droplets ejected from the nozzles 122 in the row 172 andthe ink droplets ejected from the nozzles 122 in the row 174 areparallel to one another resulting in an improved print quality.

[0159] Also, as shown in FIG. 34 of the drawings, the substrate 116 hasbond pads 176 arranged thereon which provide the electrical connections,via the pads 156, to the actuators 128 of the nozzle assemblies 110.These electrical connections are formed via the CMOS layer (not shown).

[0160] Referring to FIG. 36 of the drawings, a development of theinvention is shown. With reference to the previous drawings, likereference numerals refer to like parts, unless otherwise specified.

[0161] In this development, a nozzle guard 180 is mounted on thesubstrate 116 of the array 114. The nozzle guard 180 includes a bodymember 182 having a plurality of passages 184 defined therethrough. Thepassages 184 are in register with the nozzle openings 124 of the nozzleassemblies 110 of the array 114 such that, when ink is ejected from anyone of the nozzle openings 124, the ink passes through the associatedpassage 184 before striking the print media.

[0162] The body member 182 is mounted in spaced relationship relative tothe nozzle assemblies 110 by limbs or struts 186. One of the struts 186has air inlet openings 188 defined therein.

[0163] In use, when the array 114 is in operation, air is chargedthrough the inlet openings 188 to be forced through the passages 184together with ink travelling through the passages 184.

[0164] The ink is not entrained in the air as the air is charged throughthe passages 184 at a different velocity from that of the ink droplets164. For example, the ink droplets 164 are ejected from the nozzles 122at a velocity of approximately 3 m/s. The air is charged through thepassages 184 at a velocity of approximately 1 m/s.

[0165] The purpose of the air is to maintain the passages 184 clear offoreign particles. A danger exists that these foreign particles, such asdust particles, could fall onto the nozzle assemblies 110 adverselyaffecting their operation. With the provision of the air inlet openings88 in the nozzle guard 180 this problem is, to a large extent, obviated.

[0166] Referring now to FIGS. 37 to 39 of the drawings, a process formanufacturing the nozzle assemblies 110 is described.

[0167] Starting with the silicon substrate or wafer 116, the dielectriclayer 118 is deposited on a surface of the wafer 116. The dielectriclayer 118 is in the form of approximately 1.5 microns of CVD oxide.Resist is spun on to the layer 118 and the layer 118 is exposed to mask200 and is subsequently developed.

[0168] After being developed, the layer 118 is plasma etched down to thesilicon layer 116. The resist is then stripped and the layer 118 iscleaned. This step defines the ink inlet aperture 142.

[0169] In FIG. 37b of the drawings, approximately 0.8 microns ofaluminum 202 is deposited on the layer 118. Resist is spun on and thealuminum 202 is exposed to mask 204 and developed. The aluminum 202 isplasma etched down to the oxide layer 118, the resist is stripped andthe device is cleaned. This step provides the bond pads andinterconnects to the ink jet actuator 128. This interconnect is to anNMOS drive transistor and a power plane with connections made in theCMOS layer (not shown).

[0170] Approximately 0.5 microns of PECVD nitride is deposited as theCMOS passivation layer 120. Resist is spun on and the layer 120 isexposed to mask 206 whereafter it is developed. After development, thenitride is plasma etched down to the aluminum layer 202 and the siliconlayer 116 in the region of the inlet aperture 142. The resist isstripped and the device cleaned.

[0171] A layer 208 of a sacrificial material is spun on to the layer120. The layer 208 is 6 microns of photo-sensitive polyimide orapproximately 4 μm of high temperature resist. The layer 208 issoftbaked and is then exposed to mask 210 whereafter it is developed.The layer 208 is then hardbaked at 400° C. for one hour where the layer208 is comprised of polyimide or at greater than 300° C. where the layer208 is high temperature resist. It is to be noted in the drawings thatthe pattern-dependent distortion of the polyimide layer 208 caused byshrinkage is taken into account in the design of the mask 210.

[0172] In the next step, shown in FIG. 37e of the drawings, a secondsacrificial layer 212 is applied. The layer 212 is either 2 μm ofphotosensitive polyimide, which is spun on, or approximately 1.3 μm ofhigh temperature resist. The layer 212 is softbaked and exposed to mask214. After exposure to the mask 214, the layer 212 is developed. In thecase of the layer 212 being polyimide, the layer 212 is hardbaked at400° C. for approximately one hour. Where the layer 212 is resist, it ishardbaked at greater than 300° C. for approximately one hour.

[0173] A 0.2 micron multi-layer metal layer 216 is then deposited. Partof this layer 216 forms the passive beam 160 of the actuator 128.

[0174] The layer 216 is formed by sputtering 1,000 Å of titanium nitride(TiN) at around 300° C. followed by sputtering 50 Å of tantalum nitride(TaN). A further 1,000 Å of TiN is sputtered on followed by 50 Å of TaNand a further 1,000 Å of TiN.

[0175] Other materials which can be used instead of TiN are TiB₂, MoSi₂or (Ti, Al)N.

[0176] The layer 216 is then exposed to mask 218, developed and plasmaetched down to the layer 212 whereafter resist, applied for the layer216, is wet stripped taking care not to remove the cured layers 208 or212.

[0177] A third sacrificial layer 220 is applied by spinning on 4 μm ofphotosensitive polyimide or approximately 2.6 μm high temperatureresist. The layer 220 is softbaked whereafter it is exposed to mask 222.The exposed layer is then developed followed by hardbaking. In the caseof polyimide, the layer 220 is hardbaked at 400° C. for approximatelyone hour or at greater than 300° C. where the layer 220 comprisesresist.

[0178] A second multi-layer metal layer 224 is applied to the layer 220.The constituents of the layer 224 are the same as the layer 216 and areapplied in the same manner. It will be appreciated that both layers 216and 224 are electrically conductive layers.

[0179] The layer 224 is exposed to mask 226 and is then developed. Thelayer 224 is plasma etched down to the polyimide or resist layer 220whereafter resist applied for the layer 224 is wet stripped taking carenot to remove the cured layers 208, 212 or 220. It will be noted thatthe remaining part of the layer 224 defines the active beam 158 of theactuator 128.

[0180] A fourth sacrificial layer 228 is applied by spinning on 4 μm ofphotosensitive polyimide or approximately 2.6 μm of high temperatureresist. The layer 228 is softbaked, exposed to the mask 230 and is thendeveloped to leave the island portions as shown in FIG. 9k of thedrawings. The remaining portions of the layer 228 are hardbaked at 400°C. for approximately one hour in the case of polyimide or at greaterthan 300° C. for resist.

[0181] As shown in FIG. 371 of the drawing a high Young's modulusdielectric layer 232 is deposited. The layer 232 is constituted byapproximately 1 μm of silicon nitride or aluminum oxide. The layer 232is deposited at a temperature below the hardbaked temperature of thesacrificial layers 208, 212, 220, 228. The primary characteristicsrequired for this dielectric layer 232 are a high elastic modulus,chemical inertness and good adhesion to TiN.

[0182] A fifth sacrificial layer 234 is applied by spinning on 2 μm ofphotosensitive polyimide or approximately 1.3 μm of high temperatureresist. The layer 234 is softbaked, exposed to mask 236 and developed.The remaining portion of the layer 234 is then hardbaked at 400° C. forone hour in the case of the polyimide or at greater than 300° C. for theresist.

[0183] The dielectric layer 232 is plasma etched down to the sacrificiallayer 228 taking care not to remove any of the sacrificial layer 234.

[0184] This step defines the nozzle opening 124, the lever arm 126 andthe anchor 154 of the nozzle assembly 110.

[0185] A high Young's modulus dielectric layer 238 is deposited. Thislayer 238 is formed by depositing 0.2 μm of silicon nitride or aluminumnitride at a temperature below the hardbaked temperature of thesacrificial layers 208, 212, 220 and 228.

[0186] Then, as shown in FIG. 37p of the drawings, the layer 238 isanisotropically plasma etched to a depth of 0.35 microns. This etch isintended to clear the dielectric from the entire surface except the sidewalls of the dielectric layer 232 and the sacrificial layer 234. Thisstep creates the nozzle rim 136 around the nozzle opening 124 which“pins” the meniscus of ink, as described above.

[0187] An ultraviolet (UV) release tape 240 is applied. 4 μm of resistis spun on to a rear of the silicon wafer 116. The wafer 116 is exposedto mask 242 to back etch the wafer 116 to define the ink inlet channel148. The resist is then stripped from the wafer 116.

[0188] A further UV release tape (not shown) is applied to a rear of thewafer 16 and the tape 240 is removed. The sacrificial layers 208, 212,220, 228 and 234 are stripped in oxygen plasma to provide the finalnozzle assembly 110 as shown in FIGS. 37r and 38 r of the drawings. Forease of reference, the reference numerals illustrated in these twodrawings are the same as those in FIG. 30 of the drawings to indicatethe relevant parts of the nozzle assembly 110. FIGS. 40 and 41 show theoperation of the nozzle assembly 110, manufactured in accordance withthe process described above with reference to FIGS. 37 and 38, and thesefigures correspond to FIGS. 31 to 34 of the drawings.

[0189] It would be appreciated by a person skilled in the art thatnumerous variations and/or modifications may be made to the presentinvention as shown in the specific embodiments without departing fromthe spirit or scope of the invention as broadly described. The presentembodiments are, therefore, to be considered in all respects to beillustrative and not restrictive.

We claim:
 1. A micro-electromechanical fluid ejection device that comprises a substrate that defines a fluid inlet channel and incorporates a wafer and CMOS layers positioned on the wafer; a wall that extends from the substrate and bounds the fluid inlet channel; an elongate actuator that is connected at one end to the CMOS layers, an opposite end of the actuator being displaceable towards and away from the substrate on receipt of an electrical signal from the CMOS layers; and a nozzle that is connected to said opposite end of the actuator, the nozzle having a crown portion and a skirt portion that depends from the crown portion, the crown portion defining a fluid ejection port and the skirt portion being positioned so that the nozzle and the wall define a chamber in fluid communication with the fluid inlet channel and a volume of the fluid chamber is reduced and subsequently enlarged as the nozzle is driven towards and away from the nozzle chamber by the actuator to eject fluid from the fluid ejection port.
 2. A micro-electromechanical fluid ejection device as claimed in claim 1, in which an edge of the skirt portion is positioned adjacent an edge of the wall such that, when the chamber is filled with liquid, a meniscus is pinned by the edges of the skirt portion and the wall to define a fluidic seal that inhibits the egress of liquid from between the wall and the skirt as liquid is ejected from the fluid ejection port.
 3. A micro-electromechanical fluid ejection device as claimed in claim 1, in which the crown portion includes a rim that defines the fluid ejection port, the rim providing an anchor point for a meniscus that is formed in the fluid ejection port when the chamber is filled with liquid.
 4. A micro-electromechanical fluid ejection device as claimed in claim 1, in which an arm interconnects said opposite end of the actuator and the nozzle.
 5. A micro-electromechanical fluid ejection device as claimed in claim 4, in which the actuator includes a pair of active beams that are anchored and electrically connected to the CMOS layers and a flexible passive structure that is anchored to and electrically insulated from the CMOS layers, both the active beams and the passive structure being connected to the arm, the active beams defining a heating circuit and being of a thermally expandable material and the passive structure being interposed between the active beams and the substrate such that, when the active beams are heated by an electrical current, which is subsequently cut off, the active beams expand and contract, causing said opposite end of the actuator and thus the arm and the nozzle to be driven towards and away from the substrate.
 6. A micro-electromechanical fluid ejection device as claimed in claim 5, in which the passive structure is in the form of a pair of passive beams of the same material as the active beams, the active beams being spaced from the passive beams so that spacing between the active beams and the passive beams is greater than one percent of a length of the actuator and less than twenty percent of the length of the actuator.
 7. A micro-electromechanical fluid ejection device which comprises a substrate that defines a plurality of fluid inlet channels and incorporates a wafer and CMOS layers positioned on the wafer; walls that extend from the substrate to bound respective fluid inlet channels; elongate actuators that are connected at one end to the CMOS layers, an opposite end of each actuator being displaceable towards and away from the substrate on receipt of an electrical signal from the CMOS layers; and nozzles that are connected to respective said opposite end of the actuators, each nozzle having a crown portion and a skirt portion that depends from the crown portion, the crown portion defining a fluid ejection port and the skirt portion being positioned so that the nozzle and a respective wall define a chamber in fluid communication with the fluid inlet channel and a volume of the fluid chamber is reduced and subsequently enlarged as the nozzle is driven towards and away from the nozzle chamber by the actuator to eject fluid from the fluid ejection port. 